Roll out dough 1/4 inch thick. Cut into 3 inch rounds (should be about 20 rounds total). Spoon a tablespoon of the tuna mixture onto the top half of each round (using 10 rounds). Moisten the edges of these 10 rounds with water and place each of the remaining 10 rounds over each tuna-layer round. Press edges together with the tines of a fork and prick the tops to vent the dough. Place on a cookie sheet.